ALASKA NEMERTEANS 7 



General considerations in regard to the anatomical peculiar- 

 ities of the Nemerteans described below are reserved for a 

 future paper. My reason for postponing this important duty in 

 connection with the study of the collection is that since this 

 article was written, extensive collections of Nemerteans from 

 the west and northwest coasts of America and the Pacific Ocean 

 have been placed in my hands. These collections will doubt- 

 less include other forms than those collected on the Harriman 

 Expedition, and it seems desirable that as many as possible be 

 studied before drawing any general conclusions in regard to the 

 anatomical peculiarities presented by the Alaska forms. 



KEYS TO GROUPS AND SPECIES. 



For convenience in determination, the species at present 

 known from the northwest coast of America may be arranged 

 in the following analytical table, based mainly on superficial 

 and easily distinguishable characters. 



A. Proboscis without stylets. Mouth posterior to brain. Intestinal 

 caecum absent. 

 a. Lateral nerves external to musculature of body walls. 



Protonemertea. 

 aa. Lateral nerves imbedded in or between muscular layers of body 



walls b. 



b. Musculature of body walls in two main layers, to which an 

 inner circular layer is sometimes added in the esophagal 



region. Cerebral sense-organs absent Mesonemertea. 



bb. Musculature of body walls in three main layers, of which the 

 inner is longitudinal. Cerebral sense-organs present. 



Heteronemertea. 

 AA. Proboscis with stylets. Mouth in front of brain, usually opening 

 with proboscis in a single terminal or subterminal pore. In- 

 testinal caecum present. Lateral nerves internal to muscular 

 layers of body walls Metanemertea. 



Order PROTONEMERTEA. 



Body remarkably long, soft, and fragile. Head distinctly marked 

 off from body, usually broader than neck, often flattened dorso-ven- 

 trally Carinella^ p. 1 1 . 



1. Body very soft, attaining a length of upwards of 2 meters, deep red or 

 bright vermilion C. speciosa^ p. ii 



